Prediction Method for Annular Pressure Buildup in Deepwater Wells Based on Fluid Solid Phase Deposition

To address the risk of annular pressure relief channel blockage caused by solid deposition in the B and C annulus of deepwater wells, solid deposition tests were conducted on deepwater drilling fluid systems. The test results provided the solid settling heights of different drilling fluid systems and the post-settling solid seepage characteristics. Based on the parameters of solid seepage characteristics and considering the impact of solid deposition in annular fluids, a predictive analysis method for annular pressure buildup under seepage conditions was established, and case studies were performed. The results indicate that the settling height showed the following trend: oil-based drilling fluid > EZFLOW drilling fluid > HEM drilling fluid. In contrast, the post-settling solid permeability exhibited the opposite trend, EZFLOW drilling fluid > HEM drilling fluid > oil-based drilling fluid, with the maximum permeability reaching 2216 mD. Under the condition of solid deposition in annular fluids, as the viscosity of annular fluids decreases and the formation permeability and open-hole section length increase, the viscous forces of fluid flow decrease, and the seepage contact area with the formation increase, leading to an increase in annular fluid seepage flow. Reducing the viscosity of drilling fluids and increasing the open-hole section length of the cementing can enhance the pressure release capability of the B and C annulus in deepwater wells. However, due to the influence of solid deposition, the seepage flow rate is significantly lower than the pressure reduction rate under non-solid deposition conditions, and there is a risk of pressure relief failure after solid settlement.